The invention relates to a process for operating permanently excited single-phase alternating current machines.
One embodiment of a permanently excited single-phase alternating current machine is the transverse flux machine. These machines are permanently excited synchronous machines with a high power density combined with very low losses from the armature winding. Powered by inverse rectifiers, these machines will in the near future probably replace the direct current drive in many and varied fields of application, such as direct drives with a very high power density, traction drives with the correct distribution of drive momentum to various drive assemblies and with a high level of efficiency, and linear drives.
The principle of the transverse flux machine is based on the fact that, due to the special layout of the magnetic circuit, the usable flux runs transverse to the direction of motion. The forms of the armature winding thereby possible--annular windings in the circumferential direction--permit a high power density with a small armature through-flow and a small pole pitch. This results in very minor losses, which increases efficiency and substantially simplifies cooling of the machine. The transverse flux machine has a further advantage in the field weakening range, where, with a constant power supply, a large r.p.m. range can be covered. In the field weakening range of a transverse flux machine, the range referred to is the one where the internal voltage of the machine exceeds the intermediate circuit voltage. In DE-OS 37 05 089 A1, a circuit concept for the power supply of a double-strand transverse flux machine is described. The inverse rectifier here consists of two 4-quadrant plates. The inverse rectifier is timed in pulsed mode operation in order to adapt the voltage. The direct current can therefore be obtained from the three-phase mains via an unregulated converter. If accelerated commutation is desired, avoiding pulsed mode operation, the circuit has to be enlarged. A direct current actuator controls the effective voltage in the working phase. The level adjuster forms the commutation voltage which is applied to the inverse rectifier via the direct current actuator. The level adjuster can in this case adjust the commutation voltage as a function of various parameters, such as the r.p.m. or load current, for example.
The disadvantage of this circuit concept is that an economical arrangement of the frequency converter and optimum adaptation to user requirements, exploiting all the advantages of the transverse flux machine, are not possible.